The present invention generally relates to an image recording apparatus and an exchanging unit used in the same, and more particularly to an image recording apparatus in which an electrophotography process is performed so that the image is formed, and an exchanging unit which is detachably provided in the image recording apparatus.
A conventional image recording apparatus such as a copy machine and a facsimile, for example, has a photo sensitive medium and records the image in accordance with an electrophotography process. In this type of image recording apparatus, a charger unit, a developer device, a transfer unit, a cleaning device and so on are arranged around the photo sensitive medium. A light beam emitted from a laser unit modulated in accordance with the image data scans a surface of the photo sensitive medium between the charger unit and the developer device. That is, an exposure process is performed by the light beam which scans the photo sensitive medium. An optical system which performs the exposure process has various optical elements such as lenses and mirrors. All of the optical elements are fixed on a base so that a relative position of each optical element is prevented from changing. In addition, it is easy for the optical element close to the developer device to become dirty due to the toner scattered from the developer device. Thus, it is necessary for the optical element close to the developer device to be exchanged or cleaned at a predetermined time.
On the other hand, the image recording apparatus having an exchanging unit which includes the developer device, the charger unit and so on, has been proposed. The exchanging unit having the developer device is exchanged for a new one, for example, when the amount of toner in the developer device is less than a predetermined amount. In another case, the exchanging unit having the photo sensitive medium is exchanged for a new one, for example, when the photo sensitive medium has been used for a predetermined time.
The exchanging unit may be provided with one or a plurality of the optical elements in the optical system for performing the exposure process and it is necessary to exchange this unit at a predetermined time. In this case, when the exchanging unit is exchanged for a new one, the optical elements are also exchanged at the same time. Thus, it is easy for the optical elements to be exchanged at a predetermined time.
However, the exchanging unit must be detachable from the image recording apparatus so that a relative position of the exchanging unit with respect to the image recording apparatus changes slightly. Thus, it is difficult to accurately determine the relative position of each of the optical elements provided in the exchanging unit with respect to the other optical elements in the optical system for performing the exposure process. For example, when an incident position on the optical element (for example, a mirror), at which the light beam for scanning the photo sensitive medium is incident, changes from a regular position, the scanning line is curved, for example, in accordance with a characteristic as shown in FIG. 1. When the scanning line is curved, the quality of the image formed by the image recording apparatus deteriorates.